This is a rematch of last season's NFC divisional playoff game, which San Francisco won 36-32 on Smith's 14-yard touchdown pass to Vernon Davis with nine seconds left.

Smith may not be starting this time after missing Monday's 32-7 win over Chicago because of the concussion he suffered Nov. 11 against St. Louis. Kaepernick impressed in his first career start, going 16 of 23 for 243 yards with two touchdowns and no turnovers against a Bears defense that had forced 30 in its first nine games.

"I wanted to come out and show what I'm capable of and show that I can be a starter," said Kaepernick, a second-year player who starred collegiately at Nevada. "That's what I've been trying to prove since I've been in the league."

The once-maligned Smith has been no slouch himself this season for the West-leading Niners (7-2-1). He's completing 70.0 percent of his passes with 13 touchdowns and five interceptions, compiling a career-best passer rating of 104.1 that ranks third in the NFL.

But coach Jim Harbaugh, who had a follow-up with doctors Tuesday after undergoing a minor procedure last week to correct an irregular heartbeat, has done little to defuse the buzz regarding a possible quarterback controversy. Harbaugh simply said San Francisco would go with "the hot hand" and declined Friday to announce a starter.

Although Harbaugh expects Smith to be medically cleared to play, the coach said the team could change quarterbacks from week to week, and even during the course of a game.

"That's up to the coaches," said Davis, who caught six passes from Kaepernick on Monday for 83 yards and a touchdown. "That's their decision. I'll let them decide and they always call the shots."

The Saints (5-5) are in the midst of a turnaround that seemed improbable after an 0-4 start. They have won three straight and five of six after a 38-17 victory at Oakland last Sunday, climbing within one game of the last NFC wild-card spot.

A tough remaining schedule still blocks New Orleans' road to a fourth straight playoff berth. San Francisco is the first of three consecutive division leaders the Saints will face, as games with Atlanta and the New York Giants await.

"We've got miles to go," said assistant head coach Joe Vitt, who is 3-1 since returning from a six-game suspension. "We're nowhere near where anyone on this team wants to be. That's why every practice and every meeting and every chance you have to get better is critical. This is a marathon."

New Orleans' passing game has been consistent all season, with Drew Brees' 28 TD passes leading the league and his 306.6 yards per game ranking second. Now, he's getting help from the running game. The Saints have run for 140-plus yards in three straight games even without Darren Sproles (broken hand). They ran for 100 once in the first seven games.

More improvement could be on the way as Sproles practiced this week and should play Sunday. In his absence, the three-headed attack of Pierre Thomas, Mark Ingram and Chris Ivory combined for 419 rushing yards in the last three games.

"With the early struggles we had in the run game, we just kept at it," center Brian de la Puente said. "We stressed the little things. We knew we were close the whole time. We are at a point right now where we're very confident in our run game."

The Saints' vaunted offense -- tied for fourth in the NFL at 28.7 points per game -- will face one of its steepest challenges. San Francisco's defense has allowed the fewest points (13.4 per game) and ranks No. 2 overall, giving up an average of 293.9 total yards.

Aldon Smith has recorded 10 1/2 of his league-leading 15 sacks over the last four games after getting 5 1/2 against Chicago. He's one reason the 49ers haven't allowed a 300-yard passer since letting Brees throw for 462 and four TDs in the playoff win.

Smith threw for three scores and ran for one in that game, and he would be facing the NFL's lowest-ranked defense if he takes the field Sunday. The Saints have allowed at least 400 yards in all 10 games, but they've held the opposition to an average of 19.0 points in three games this month after allowing 30.9 through October.

They'll be matched up against Frank Gore and the NFL's top rushing offense, with Gore averaging 83.1 of San Francisco's 165.3 yards per game.

The Saints have won the last six regular-season meetings.

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Scouting Report

49ers-Saints: What to watch

After watching film of both teams, Scouts Inc. breaks down key elements of the Week 12 49ers-Saints matchup.

" Take what the defense gives you: There may be no quarterback who does a better job of taking what the defense gives than the Saints' Drew Brees. He is a great decision-maker and one of the best at distributing the ball to all of his receivers and not forcing the issue. The Saints can't afford to get greedy or impatient. The 49ers are one of the best-tackling teams in the NFL, as evidenced by their ability to prevent explosive plays and limit their opponents' yards after the catch.

Research Notes

The 49ers sacked or put Drew Brees under duress on 20 dropbacks (29.9 percent) in last season's NFC Divisional Playoffs. That was Brees' most dropbacks sacked or under duress and his fourth-highest rate in a game since the start of 2009.

The Saints have dropped back to pass 39.4 percent of the time with Mark Ingram in the game this season, compared to 72.8 percent of the time when one of the other Saints running backs is on field. The more run-heavy approach with Ingram has opened up the play-action game for Brees.

Drew Brees has a league-best 13 touchdowns on throws at least 15 yards downfield this season, while the 49ers defense has allowed the fewest completions on such passes, along with one touchdown. Brees challenged their secondary with mixed results in last season's NFC Divisional Playoffs, completing 3-of-9 passes with two touchdowns and two interceptions.